As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AUXILIARY BATTERY TEMP AT 38 PRIOR TO T/O, IN CRUISE, SLOWLY ROSE TO 55 WITH A LOAD OF 25 PERCENT AND BOTH TEMP CAUTION LIGHT ILLUMINATING. BATTERY SELECTED OFF AND TEMP INCREASED TO 75 DEGREES PRIOR TO LANDING. MAINTENANCE NOTIFIED OF RT TRIP TO REPLACE AUXILIARY BATTERY.